Curable epoxy resin composition comprising fillers

ABSTRACT

Curable epoxy resin compositions comprising 
     (a) an epoxy resin having on average more than one epoxide group in the molecule, 
     (b) an epoxy resin curing agent in an amount sufficient for full curing of the epoxy resin, 
     (c) wollastonite having an average particle size of less than 100 μm in an amount of 10 to 350 parts by weight per 100 parts by weight of the sum of components (a) and (b), 
     (d) a quartz/kaolinite mixture having an average particle size of less than 100 μm in an amount of 10 to 350 parts by weight per 100 parts by weight of the sum of components (a) and (b), the content of components (c) and (d) together not being greater than 360 parts by weight, and, if appropriate, 
     (e) customary additives, are suitable for the production of mouldings having high-glass surfaces.

This application is a division of application Ser. No. 08/647,077, filedMay 8,1996, now U.S. Pat. No. 5,705,541, which is a continuation ofapplication Ser. No. 08/272,717,filed Jul. 8, 1994, now abandoned.

The present invention relates to a curable epoxy resin compositioncomprising wollastonite and a quartz/kaolinite mixture, which issuitable for the production of mouldings having high-gloss surfaces.

It is known to add fillers to curable epoxy resin compositions in orderto obtain moulded materials therefrom which have improved mechanicalproperties. For production of mouldings with high-gloss properties fromsynthetic resin compositions, it is desirable for the mouldings also tohave good mechanical and good thermal properties, in addition to ahigh-gloss surface.

To increase the surface gloss of mouldings, epoxy resins have hithertomerely been applied in the form of powder coatings to existing surfaces,onto which a metal has then been vapour-deposited Such a process isdescribed, for example, in EP-A-0 244996.

It has now been found that if curable epoxy resin compositions filledwith wollastonite and a quartz/kaolinite mixture are used, mouldedmaterials or coatings having both good mechanical properties andhigh-gloss surfaces onto which metals can be vapour-deposited directlyare obtained by curing.

The present invention thus relates to a curable epoxy resin compositioncomprising

(a) an epoxy resin having on average more than one epoxide group in themolecule,

(b) an epoxy resin curing agent in an amount sufficient for full curingof the epoxy resin,

(c) wollastonite having an average particle size of less than 100 μm inan amount of 10 to 350 parts by weight per 100 parts by weight of thesum of components (a) and (b),

(d) a quartz/kaolinite mixture having an average particle size of lessthan 100 μm in an amount of 10 to 350 parts by weight per 100 parts byweight of the sum of components (a) and (b), the content of components(c) and (d) together not being greater than 360 parts by weight, and, ifappropriate,

(e) customary additives.

The epoxy resins customary in the epoxy resin industry can be used asepoxy resin (a) for the preparation of the epoxy resin compositionsaccording to the invention. Examples of epoxy resins are:

I) Polyglycidyl and poly(β-methylglycidyl)esters obtainable by reactionof a compound having at least two carboxyl groups in the molecule andepichlorohydrin or β-methylepichlorohydrin. The reaction isadvantageously carried out in the presence of bases.

Aliphatic polycarboxylic acids can be used as the compound having atleast two carboxyl groups in the molecule. Examples of suchpolycarboxylic acids are oxalic acid, succinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid or dimerized ortrimerized linoleic acid. However, it is also possible to employcycloaliphatic polycarboxylic acids, for example tetrahydrophthalicacid, 4-methyltetrahydrophthalic acid, hexahydrophthalic acid or4-methylhexahydrophthalic acid. Aromatic polycarboxylic acids, forexample phthalic acid, isophthalic acid or terephthalic acid, canfurthermore be used.

II) Polyglycidyl or poly(β-methylglycidyl)ethers obtainable by reactionof a compound having at least two free alcoholic hydroxyl groups and/orphenolic hydroxyl groups and epichlorohydrin or β-methylepichlorohydrinunder alkaline conditions or in the presence of an acid catalyst withsubsequent treatment with an alkali.

The glycidyl ethers of this type are derived, for example, from acyclicalcohols, such as from ethylene glycol, diethylene glycol and higherpoly(oxyethylene) glycols, propane-1,2-diol or poly(oxypropylene)glycols, propane-1,3-diol, butane-1,4diol, poly(oxytetramethylene)glycols, pentane-1,5-diol, hexane-1,6-diol, hexane-2,4,6-triol,glycerol, 1,1,1-trimethylolpropane, pentaerythritol or sorbitol and frompolyepichlorohydrins. However, they are also derived, for example, fromcycloaliphatic alcohols, such as 1,4-cyclohexanedimethanol,bis(4-hydroxycyclohexyl)methane or 2,2-bis(4-hydroxycyclohexyl)propane,or they have aromatic nuclei, such as N,N-bis(2-hydroxyethyl)aniline orp,p′-bis(2-hydroxyethylamino)diphenylmethane. The glycidyl ethers canalso be derived from mononuclear phenols, for example from resorcinol orhydroquinone, or they are based on polynuclear phenols, such as, forexample, bis(4-hydroxyphenyl)methane, 4,4′-dihydroxybiphenyl,bis(4-hydroxyphenyl) sulfone, 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane,2,2-bis(4-hydroxyphenyl)propane and2,2-bis(3,5)bromo-4-hydroxyphenyl)propane, and from novolaks obtainableby condensation of aldehydes, such as formaldehyde, acetaldehyde,chloral or furfuraldehyde, with phenols, such as phenol, or with phenolswhich are substituted in the nucleus by chlorine atoms or C₁-C₉alkylgroups, such as, for example, 4-chlorophenol, 2-methylphenol or4-tert-butylphenol, or by condensation with bisphenols such as those ofthe type as defined above.

III) Poly(N-glycidyl) compounds obtainable by dehydrochlorination of thereaction products of epichlorohydrin with amines which have at least twoamine hydrogen atoms. These amines are, for example, aniline,n-butylamine, bis(4-aminophenyl)methane, m-xylylenediamine orbis(4-methylaminophenyl)methane.

However, the poly(N-glycidyl) compounds also include triglycidylisocyanurate, N,N′-diglycidyl derivatives of cycloalkyleneureas, such asethyleneurea or 1,3-propyleneurea, and diglycidyl derivatives ofhydantoins, such as of 5,5-dimethylhydantoin.

IV) Cycloaliphatic epoxy resins, for example bis(2,3-epoxycyclopentyl)ether, 2,3-epoxy-cyclopentyl glycidyl ether,1,2-bis(2,3-epoxycyclopentyloxy)ethane or 3,4-epoxy-cyclohexylmethyl3′,4′-epoxycyclohexanecarboxylate.

However, epoxy resins in which the 1,2-epoxide groups are bonded todifferent heteroatoms or functional groups can also be used; thesecompounds include, for example, the N,N,O-triglycidyl derivative of4-aminophenol, the glycidyl ether-glycidyl ester of salicylic acid,N-glycidyl-N′-(2-glycidyloxypropyl)-5,5-dimethylhydantoin or2-glycidyloxy-1,3-bis(5,5-dimethyl-1-glycidylhydantoin-3-yl)propane.

An aromatic epoxy resin, i.e. an epoxy compound which contains one ormore aromatic rings in the molecule, is preferably used for thepreparation of the epoxy resin compositions according to the invention.

In particular, a bisphenol diglycidyl ether or an epoxy-novolak resin,particularly preferably an epoxyphenol- or an epoxycresol-novolak resin,is used for the preparation of the epoxy resin compositions according tothe invention.

The curing agents customary in the epoxy resin industry, for examplepolycarboxylic acids and anhydrides thereof, dicyandiamide, polyamines,polyaminoamides, adducts containing amino groups, aliphatic or aromaticpolyols or curing agents having a catalytic action, can be employed asthe epoxy resin curing agent (b) for the epoxy resin compositionsaccording to the invention.

Suitable polycarboxylic acids for curing the epoxy resin compositionsaccording to the invention are, for example, aliphatic polycarboxylicacids, such as maleic acid, oxalic acid, succinic acid, nonyl- ordodecylsuccinic acid, glutaric acid, adipic acid, pimelic acid, subericacid, azelaic acid or dimerized or trimerized linoleic acid,cycloaliphatic polycarboxylic acids, such as, for example,tetrahydrophthalic acid, methylendomethylenetetrahydrophthalic acid,hexachloroendomethylenetetrahydrophthalic acid,4-methyltetrahydrophthalic acid, hexahydrophthalic acid or4-methylhexahydrophthalic acid, or aromatic polycarboxylic acids, suchas, for example, phthalic acid, isophthalic acid, terephthalic acid,trimellitic acid, pyromellitic acid orbenzophenone-3,3′,4,4′-tetracarboxylic acid, and the anhydrides of thepolycarboxylic acids mentioned.

Polyamines which can be employed for curing the abovementioned epoxyresin compositions are aliphatic, cycloaliphatic, aromatic orheterocyclic amines, such as, for example, ethylenediamine,propane-1,2-diamine, propane-1,3-diamine, N,N-diethylethylenediamine,hexamethylenediamine, diethylenetriamine, triethylenetetramine,tetraethylenepentamine, N-(2-hydroxyethyl)-, N-(2-hydroxypropyl)- andN-(2-cyanoethyl)diethyltriamine, 2,2,4-trimethylhexane-1,6-diamine,2,3,3,-trimethylhexane-1,6-diamine, N,N-dimethyl- andN,N-diethylpropane-1,3-diamine, ethanolamine, m- and p-phenylenediamine,bis(4-aminophenyl)methane, aniline-formaldehyde resin,bis(4-aminophenyl) sulfone, m-xylylenediamine,bis(4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane,2,2-bis(4-amino-3-methylcyclohexyl)propane,3-aminomethyl-3,5,5-trimethylcyclohexylamine (isophoronediamine) andN-(2-aminoethyl)piperazine.

Suitable polyaminoamides for curing the abovementioned epoxy resincompositions are, for example, the reaction products obtained byreaction of polycarboxylic acids, preferably of di- or trimerized fattyacids, with polyamines, preferably aliphatic polyamines, in a molarexcess, such as are described, for example, in Handbook of Epoxy Resins,1967, pages 10-2 to 10-10 by H. Lee and K. Neville.

Amino group-containing adducts which are obtained from an amine and apolyepoxy compound and which function as curing agents for epoxy resinsare also known and can be employed for curing the abovementioned epoxyresin compositions, and are obtained, for example, by reaction of epoxyresins with polyamines in an equivalent excess. Such aminogroup-containing adducts are described in more detail, for example, inU.S. Pat. Nos. 3,538,184; 4,330,659; 4,500,582 and 4,540,750.

Suitable aliphatic polyols for curing the abovementioned epoxy resincompositions are, for example, ethylene glycol, diethylene glycol andhigher poly(oxyethylene) glycols, propane-1,2-diol or poly(oxypropylene)glycols, propane-1,3-diol, butane-1,4-diol, poly(oxytetramethylene)glycols, pentane-1,5-diol, hexane-1,6-diol, hexane-2,4,6-triol,glycerol, 1,1,1-trimethylolpropane, pentaerythritol or sorbitol.

Aromatic polyols which can be employed for curing the abovementionedepoxy resin compositions are, for example, mononuclear phenols, such asresorcinol, hydroquinone or N-N-bis(2-hydroxyethyl)aniline, orpolynuclear phenols, such asp,p′-bis(2-hydroxyethylamino)diphenylmethane,bis(4-hydroxyphenyl)methane, 4,4′-dihydroxybiphenyl,bis(4-hydroxyphenyl) sulfone, 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane,2,2-bis(4-hydroxyphenyl)propane and2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane, and novolaks obtainable bycondensation of aldehydes, such as formaldehyde, acetaldehyde, chloralor furfuraldehyde, with phenols, such as phenol, or with phenols whichare substituted in the nucleus by chlorine atoms or C₁-C₉alkyl groups,such as, for example, 4-chlorophenol, 2-methylphenol or4-tert-butylphenol, or by condensation with bisphenols, such as those ofthe type defined above.

It is also possible to use curing agents having a catalytic action forcuring the epoxy resin compositions, such as tertiary amines, forexample 2,4,6tris(dimethylaminoethyl)phenol and other Mannich bases,N-benzyldimethylamine and triethanolamine; alkali metal alkoxides ofalcohols, for example the sodium alcoholate of2,4-dihydroxy-3-hydroxymethylpentane; tin salts of alkanoic acids, forexample tin octanoate; and Friedel-Crafts catalysts, for example borontrifluoride and its complexes and chelates which are obtained byreaction of boron trifluoride with, for example, 1,3-diketones.

A phenolic epoxy resin curing agent is preferably used as curing agent(b) for the epoxy resin compositions according to the invention.

In particular, a cresol novolak is employed as curing agent (b).

Suitable curing accelerators can also be employed with the epoxy resincuring agents. For example, if dicyandiamide, polyaminoamides orpolycarboxylic acids and anhydrides thereof are used, tertiary amines orsalts thereof, quaternary ammonium compounds or alkali metal alkoxidescan be used as accelerators.

The amount of curing agent employed depends on the chemical nature ofthe curing agent and on the desired properties of the curablecomposition and of the cured product. The maximum amount can easily bedetermined. If the curing agent is an amine, 0.75 to 1.25 equivalents ofamine hydrogen per 1 epoxy equivalent are usually employed. Ifpolycarboxylic acids or anhydrides thereof are employed, 0.4 to 1.1equivalents of a carboxyl group or of an anhydride group per 1 epoxyequivalent are usually used. If polyphenols are used as the curingagent, 0.75 to 1.25 phenolic hydroxyl groups per 1 epoxy equivalent areemployed. Curing agents having a catalytic action are in generalemployed in amounts of 1 to 40 parts by weight per 100 parts by weightof epoxy resin.

The wollastonite used as component (c) in the epoxy resin compositionsaccording to the invention is a naturally occurring calcium silicate ofthe formula Ca₃[Si₃O₉] of needle-shaped structure having particle sizesin the micron range. Wollastonite which can be prepared syntheticallyalso has a needle-shaped structure. Wollastonite is commerciallyobtainable, for example under the name Nyad® from Nyco.

The epoxy resin compositions according to the invention preferablycomprise wollastonite having an average particle size of less than 50μm, in particular having an average particle size of less than 5 μm.Average particle size for the wollastonite is based on an equivalentspherical diameter by weight as determined by a sedigraph.

The epoxy resin compositions according to the invention furthermorecomprise wollastonite in an amount of 50 to 200 parts by weight per 100parts by weight of the sum of components (a) and (b).

The quartz/kaolinite mixture to be used as component (d) in the epoxyresin compositions according to the invention is likewise known and canbe prepared, for example, by simply mixing ground quartz with kaolinite.Kaolinite, one of the main constituents of kaolin, is commerciallyobtainable as microcrystalline aluminium silicate.

The epoxy resin compositions according to the invention preferablycomprise a quartz/kaolinite mixture in an amount of 50 to 200 parts byweight per 100 parts by weight of the sum of components (a) and (b).

The epoxy resin compositions according to the invention furthermorecomprise a quartz/kaolinite mixture which preferably consists of 5 to 95parts by weight of quartz and 95 to 5 parts by weight of kaolinite, inparticular of 20 to 80 parts by weight of quartz and 80 to 20 parts byweight of kaolinite, per 100 parts by weight of the mixture.

The quartz/kaolinite mixture which the epoxy resin compositionsaccording to the invention comprise preferably has an average particlesize of less than 50 μm, in particular less than 5 μgm. Average particlesize for the quartz/kaolinite mixture is based on an equivalentspherical diameter by number as determined by the Fraunhofer diffractionmethod.

The epoxy resin compositions according to the invention can comprise, ascustomary additives (e), other customary fillers, such as glass powderor metal powder, dyes, pigments, such as titanium dioxide, processingauxiliaries, such as lubricants, flow control agents, thixotropicagents, stabilizers, adhesion promoters between fillers and resin,curing accelerators or mould release agents.

If other customary fillers are added to the epoxy resin compositionsaccording to the invention, fillers (c) and (d) to be used according tothe invention make up at least two thirds, preferably at least threequarters, of the total amount of filler.

The epoxy resin compositions according to the invention are prepared bymethods known per se, such as with the aid of known mixing units, forexample stirrers, kneaders, rollers or, in the case of solid substances,in dry mixers.

Curing of the epoxy resin compositions according to the invention togive shaped articles, coatings or the like is carried out in the mannercustomary in the epoxy resin industry by heating, such as is described,for example, in “Handbook of Epoxy Resins”, 1967, by H. Lee and K.Neville. The curing temperature is in general between 50 and 200° C.

The epoxy resin compositions according to the invention are suitable,for example, as casting resins, laminating resins, adhesives,compression moulding compositions, coating compositions and coveringsystems for electrical and electronic components, preferably for theproduction of shaped articles or coatings having shiny surfaces, suchas, for example, headlamps. The shaped articles produced from the epoxyresin compositions according to the invention have smooth surfaces, sothat, on the basis of the good surface nature, they can be provideddirectly with a metal coating, for example by vapour deposition ofaluminium.

The present invention therefore also relates to the use of the epoxyresin composition according to the invention for the production ofmoulded materials having high-gloss surfaces.

The moulded materials or coatings produced from the epoxy resincompositions according to the invention furthermore are distinguished bya high heat stability. For example, these can be heated up to about 240°C. or even to higher temperatures over a relatively long period of timewithout distortion phenomena occurring on the moulded materials orcoatings. The moulded materials or coatings produced from the epoxyresin compositions according to the invention thus have a low expansiondifference within the moulding on heating. The low occurrence of gasevolution phenomena at elevated temperature, for example up to about240° C. or at even higher temperatures, is also advantageous in themoulded materials produced from the epoxy resin compositions accordingto the invention.

EXAMPLE

20.73 g of a solid, ground epoxycresol-novolak resin having an epoxyvalue of 4.0-4.4 equivalents/kg; 10.07 g of a phenol-novolak having ahydroxyl value of 8.0-9.0 equivalents/kg, obtainable from OccidentalChem., Belgium under the tradename Durex®33009; 35.26 g of wollastonitehaving an average particle size of 2.8 μm, obtainable from Nyco, USAunder the tradename Nyad®91250; 30.22 g of a quartz/kaolinite mixturehaving an average particle size of 1.8 μm, obtainable from Hoffmann &Söhne, Germany under the tradename Aktisil®EM; 0.4 g of2-ethylimidazole; 0.2 g of β-glycidyloxypropyltrimethoxysilane (SilaneA-187 from Union Carbide); 0.4 g of carbon black (Elftex 460); 0.8 g ofOP wax from Hoechst and 0.5 g of Ca stearate are compounded on aBuss-Cokneader PR 46 at a temperature of 70-90° C. and ground togranules. From the granules, ISO dumbbell bars are produced for thephysical tests and test sheets of dimensions 50×40 mm are produced in ahighly polished chromium-plated mould for measurement of the gloss. Theprocessing conditions here are: injection moulding machine Bucher TS120, cylinder temperature=80/60° C., mould temperature=180/180° C. andcuring time=50 seconds. The following properties are measured on theresulting shaped articles:

Impact strength (ISO 179, method 1eU) = 5.0 kJ/m² Temperature ofdeflection under load (ISO 75, method A) = 175° C. Gloss (reflectionvalue according to DIN 67530) = 82%.

What is claimed is:
 1. A curable epoxy resin composition comprising (a)a solid epoxy resin having on average more than one epoxide group in themolecule, (b) an epoxy resin curing agent in an amount sufficient forfull curing of the epoxy resin, (c) wollastonite having a weight averageparticle size of less than 50 μm in an amount of 10 to 350 parts byweight per 100 parts by weight of the sum of components (a) and (b), (d)a quartz/kaolinite mixture having a number average particle size of lessthan 50 μm in an amount of 10 to 350 parts by weight per 100 parts byweight of the sum of components (a) and (b), the content of components(c) and (d) together not being greater than 360 parts by weight, and, ifappropriate.
 2. An epoxy resin composition according to claim 1, whichcomprises an aromatic epoxy resin as component (a).
 3. An epoxy resincomposition according to claim 1, which comprises a bisphenol diglycidylether or an epoxy-novolak resin as component (a).
 4. An epoxy resincomposition according to claim 1, which comprises an epoxyphenol- or anepoxycresol-novolak resin as component (a).
 5. An epoxy resincomposition according to claim 1, which comprises a phenolic curingagent for the epoxy resin as component (b).
 6. An epoxy resincomposition according to claim 1, which comprises a cresol-novolak ascomponent (b).
 7. An epoxy resin composition according to claim 1, whichcomprises wollastonite in an amount of 50 to 200 parts by weight per 100parts by weight of the sum of components (a) and (b).
 8. An epoxy resincomposition according to claim 1, which comprises wollastonite having anaverage particle size of less than 5 μm.
 9. An epoxy resin compositionaccording to claim 1, which comprises a quartz/kaolinite mixture in anamount of 50 to 200 parts by weight per 100 parts by weight of the sumof components (a) and (b).
 10. An epoxy resin composition according toclaim 1, which comprises a quartz/kaolinite mixture which consists of 5to 95 parts by weight of quartz and 95 to 5 parts by weight of kaoliniteper 100 parts by weight of the mixture.
 11. An epoxy resin compositionaccording to claim 10, which comprises a quartz/kaolinite mixture whichconsists of 20 to 80 parts by weight of quartz and 80 to 20 parts byweight of kaolinite per 100 parts by weight of the mixture.